1. Field of the Invention
The present invention relates to an optical playback medium and a playback method therefor.
2. Description of the Related Art
An optical playback medium is typically an optical disk, an optical card, or a similar medium. At present, there are active efforts underway to achieve high density in CD-ROMs (Compact Disc Read-Only Memories), which are playback-only optical disks. Bumps and depressions are formed in the surface of a CD-ROM substrate and a difference of intensity of light reflected from the surface when light is caused to strike the surface are sensed to recognize these surface bumps and depressions and convert them to a signal.
Referring to FIGS. 8(A) and 8(B), in an optical playback medium of the past (CD-ROM), a recorded original, known as a stamper, having bumps and depressions, is transferred to a substrate 2, which is fabricated by means of injection molding technology or the like, and a metallic film such as aluminum is formed on the top of this substrate 2 as a reflective film 4. The stamper is made by an exposure technique known as mastering, a recorded mark formed in the stamper by mastering becoming a recorded pit 3 that is a groove in the optical playback medium (CD-ROM). When doing this, the density of the recording pits 3 of the optical playback medium (CD-ROM) is established by how small a recording mark can be formed in the stamper by mastering.
However, with the recent demand for high-density, mastering is reaching a limit, which is blocking the achievement of higher-density optical media (CDROMs). To achieve high density in an optical playback medium (CD-ROM), it is necessary to have a new method that does not rely on mastering alone.